LOW NOISE Nb-SIS MIXERS AT FAR ABOVE THE GAP FREQUENCY

摘要

There are great interests in developing Nb SIS mixers because of the extremely low noise temperatures and because of the need of low local oscillator (LO) power. Several groups have demonstrated experimentally that Nb SIS mixers with integrated tuning elements can perform near the quantum noise limit up to the Nb gap frequency ( ～ 700 GHz). Beyond this frequency, a major loss will take place in the tuning elements, which are Nb/SiO_2/Nb micro-striplines, because the incoming photons can break the Cooper-pairs, thus increasing the surface resistance of the Nb strips.